A slender shaft is a long narrow cylinder with a high length to diameter ratio. It’s much longer than it is wide and provides turning services. Slender shaft can bend easily, buckle under pressure and vibrate more. They are used in industries like engineering and aerospace. Design and handling need careful attention due to their unique characteristics.
Slender shaft is a notably long and thin shaft and it requires high accuracy in machining. This kind is mainly used as a high speed spindle. To prevent this, use support fixtures, adjust cutting parameters, choose appropriate tools, and consider design changes to enhance shaft stiffness.
There are mainly two types of shaft:
- Transmission shaft: Transmission shafts transmit power between the source and the machine absorbing power; e.g. counter shaft and line shaft.
- Machine shaft: Machine shafts are the machine’s integral part, e.g., crankshaft, axle shaft.
Cause of Bending Deformation
In the CNC turning process, dealing with the cylinder shaft demands attention to prevent a bending deformation of the workpiece.
- Cutting Force: This force can cause the slender shaft to bend as it resists the cutting action. The radial cutting force (Fpy) is used in machining to understand and manage the sideways force exerted on the cutting tool during operations like turning or milling.
- Cutting heat: Cutting heat affects slender shafts during machining, leading to thermal deformation, residual stresses, material changes, poor surface finish, and accelerated tool wear. The elevated temperatures cause thermal expansion and elongation, resulting in bending and shape alterations. To manage these effects, use cooling methods, adjust cutting parameters like speed , choose suitable tool coatings, and opt for workpiece materials that resist thermal deformation.
- Poor rigidity of the slender shaft: A slender shaft can bend during machining due to cutting forces, when it lacks rigidity. This bending leads to shape and dimension accuracy.
Problems in the Turning Process
A bent shaft causes shaft rate vibration (1x) in all three axes. Depending on the location of the bend, one might also see an elevated 2x in the Axial direction. Harmonics of 1x are also possible. Be careful not to mistake a high 1x H and 1x V for unbalance.
- The workpiece is subject to cutting resistance and generates vibration and bending deformation. Reduce geometric accuracy and surface finish.
- The heat of cutting is absorbed by the workpiece during the cutting process. This can result in a large axial expansion of the workpiece . Increase bending deformation and increase vibration. Even the workpiece squeezed between the two tips. Caused by inability to process.
- The longer the ratio of long neck to neck, the greater the self gravity. Because the workpiece is at high speed. Thus, the centrifugal force generated is also larger. And the up and down jump will affect the processing quality.
- The geometric angle of the tool. The amount of cutting and processing methods are not selected. Will increase the cutting force. Deformation and vibration are exacerbated.
- The workpiece bending and vibration, the turning use a lower speed and depth of cut. Limits the increase in productive efficiency.
- The workpiece under the action of radial cutting force. The shape of the workpiece that has been machine by turning is easy to form a small end. And a large middle, and it is easy to produce a knife phenomenon.
- The machine tool is adjusted, and easy to produce cone errors. Improper Change of the fixture, easy to cause bending and produce bamboo, diamond and so on.
Conclusion
In the production of slender shaft parts, turning is the most useful element at present. Parts bending is the serious problem in CNC turning machining, which can not meet product processing requirements. Reasonable clamping is the application of the required tool geometric parameters, cutting parameters and auxiliary devices etc. It guarantees the processing requirements of slender shaft parts and then achieves high quality of the following assembly parts.
